1. Field of the Invention
This invention is concerned with methods of determining the palatability, or attractant preference, of chemical substances to fish, specifically one which can be used to screen potential chemical stimulants or attractants to be added to commercial fish baits and foodstuffs for the purpose of enhancing the palatability, acceptability, and potency of these products. In particular the method relates to exposing fish to cellulose pellets containing compounds believed to be attractants and measuring the time interval in which the fish species retains or swallows the cellulose pellet.
2. Description of Related Art
Like mammals, probably all fish use their sense of taste to assess the palatability of objects taken into their mouths. In fact, fish will readily eject objects which are neutral or offensive in taste from their mouths in a matter of seconds, whereas those which are palatable are retained, chewed, and perhaps even swallowed. In the past, numerous researchers have utilized this behavior to screen various chemical stimulants, both of a complex (e.g. the flesh of living prey) and pure (e.g. amino acids obtained from a commercial chemical supplier) nature, as potential additives for enhancing commercial fish baits and foodstuffs. In these studies palatability has been measured by comparing the feeding intensity of a target species to a plain bland basal diet versus that to the same diet flavored with the test substance(s) of interest. Thus Hidaka et al. "Taste Receptor Stimulation and Feeding Behavior in the Puffer, Fugu Pardalis I. Effect of Single Chemicals" Chem. Senses Flav., vol. 3, pp. 341-354 (1978), Ohsugi et al. "Taste Receptor Stimulation and Feeding Behavior in the Puffer, Fugu Pardalis. II. Effects Produced by Mixtures of Constituents of Clam Extracts" Chem. Senses Flav., vol. 3, pp. 355-368, (1978), and Hidaka, "Taste Stimulation and Feeding Behavior in the Puffer" Chemoreception in Fishes, Elsevier Publisher, N.Y. pp. 243-257, (1982) scored the response intensity of puffers (Fugu pardalis) to pellets of plain and flavored wheat starch on an arbitrary scale of 0-4. Using a mixture of casein, vitamins, and minerals as the basal diet, Adron and Mackie "Studies on the Chemical Nature of Feeding Stimulants for Rainbow Trout, Salmo Gairdneri" J. Fish Biol., vol. 12, pp. 303-310 (1978) determined the relative acceptability of flavored versus non-flavored diets to rainbow trout (Salmo gairdneri) by counting the number of times the fish actuated a self-feeder offering a fixed number of food pellets with each actuation. Likewise, Mackie and Adron "Identification of Inosine and Inosine 5'-Monophosphate as the Gustatory Feeding Stimulants for the Turbot, Scophthalmus Maximus" Comp. Biochem. Physiol., vol. 60A, pp. 79-83 (1978) measured the percentage of food pellets proffered which were actually eaten by the turbot (Scophthalmus maximus), whereas Mackie et al. "Chemical Nature of Feeding Stimulants for the Juvenile Dover Sole, Solea Solea (L.)" J. Fish Biol., vol. 16, pp. (1980) and Mackie and Mitchell "Further Studies on the Chemical Control of Feeding Behavior in the Dover Sole, Solea Solea" Comp. Biochem. Physiol., vol. 73A, pp. 89-93 (1982) and "Studies on the Chemical Nature of Feeding Stimulants for the Juvenile European Eel, Anguilla Anguilla (L.)" J. Fish Biol., vol. 22, pp. 425-430 (1983), measured the amount of flavored and non-flavored diet eaten before feeding cessation by the Dover sole (Solea solea) and the European eel (Anguilla anguilla), respectively. Using a similar casein-based diet, Goh and Tamura "Effect of Amino Acids on the Feeding Behavior in Red Sea Bream" Comp. Biochem. Physiol., vol. 66C, pp. 225-229 (1980), Takeda et al, "Identification of Feeding Stimulants for Juvenile Eel" Bull. Jap. Soc. Sci. Fish., vol. 50, pp. 645-651, (1984), and Takii et al, "Effects of Supplement of Feeding Stimulants to Formulated Feeds on Feeding Activity and growth of Juvenile Eel" Bull. Jap. Soc. Sci. Fish., vol. 50, pp.1039-1043 (1984), offered the red sea bream (Chrysophrys major) or the Japanese eel (Anguilla japonica) a choice between two food balls (one flavored and one not) presented together to determine whether the flavored diet was preferred. In a similar bioassay, Adams and Johnsen, "A Solid Matrix Bioassay for Determining Chemical Feeding Stimulants", Prog. Fish-Cult., vol. 48, pp. 147-149 (1986) and Johnsen and Adams U.S. Pat. No. 4,693,897 issued Sept. 15, 1987, offered Tilapia zillii a choice between two agar disks, one experimental and one reference, to establish their preference. The patent makes reference to several articles dealing with chemosensory reception or rejection by various fish.
As some of these researchers themselves admit, these methodologies have several drawbacks. The basal diet may have a taste of its own and thereby influence the experimental subject's perception of the test substance. Also, in multiple choice tests, whether a fish begins to feed on the flavored or non-flavored diet is largely a matter of which one is contacted first. Moreover, because the diet is filling and its consumption gradually lowers the subject's motivation to feed during repeated trials, the variability within these behavioral assays is undesirably high, diminishing their sensitivities. Most importantly, however, the preparation of the diets and the lengthy observations on the behavioral responses are rather labor-intensive and time-consuming. Hence, the methods themselves are sufficiently tedious to inhibit investigators from undertaking the exhaustive type of studies needed to better understand taste perception in fish and to apply this knowledge in the enhancement of commercial fish baits and feeds.